Die structure for injection molding machines



Dec. 22, 1942. L. F. MARSH 2,306,316

DIE STRUCTURE FOR INJECTION MOLDIQG MACHINES Filed Aprfl m. 1939 by 3B 17 Q r v W1 -n i k 551 I'Mars/z Patented Dec. 22, 1942' pm STRUCTURE FOR mmc'rroNMoLmNG I moms,

Iieon F. Marsh, Hudson, Mam, assignor to Reed- Prentice, Corporation, Worcester, poration of Massachusetts Mass., a cor- Ap licants April 10, 1939, Serial 1%. 268,928

- 3 Claims. (Cl. 18-42) The present invention relates to injection molding machines, particularly those employing material which is first rendered plastic by the application of heat, and is then injected under pressure into cooperating dies, one of which is mov'- able with respect to the other.

The object of the invention is to provide an improved die structure, wherein one die is provided with means for obtaining localized cooling of a portion of plasticized material sufiicient to cause its being solid enough to insure complete withdrawal of the molded material from the sta-- tlonary die, prior to its ejection from the ma-' chine. The above and other advantageous features of the invention will hereinafter more fully appear from .the following description, considered in connection with the accompanying drawing, in which- Fig. l is a sectional view of a pair of cooperating dies embodying the invention. I

Fig. 2 is a fragmentary sectional view of portions of the dies shown in Fig. 1, illustrating withdrawal of a molded article from the stationary die.

Fig. 3 is afragmentary view similar to Fig. 2, illustrating ejection of the article from the movable die.

Fig. 4 is a fragmentary view, showing a portion of a molded article in perspective.

Like reference characters refer to like parts in the different figures.

Referring to thedrawing, a stationary die I is shown as providing a sprueway 2 of increasing not shown. Runners 5 radiate from the sprueway 2, in communication with molding recesses 8 and I provided in the dies l and 8, respectively, and the movable die 3 also provides a recess 8 in alinement with the sprueway 2.

When the dies of the character shown are utilized to mold articles from thermoplastic ma-.

terial, dimculties have heretofore arisen from the fact that certain thermoplastic materials exhibit a relatively narrow temperature range in which they have the desired flow characteristics for molding. As a result, material spreading rapidly into the die recesses 8 and 1, tends to cool and solidify more rapidly than the material in the centrated. Consequently, when the, die 3 is moved away from the diel to withdraw the molded article, the material is liable tobreak .near the base of the sprue 9, as indicated in dotted lines, due to the fact that it is still in a semi-plastic condition at that point, as compared to the molded article ID.

According to the present invention, provision is made for cooling a portion of thermoplastic material disposed within the movable die in the' vicinity of the sprue 8, so that the material at that point will have cooled and solidified sufiiciently to insure that the sprue 9 will withdraw cleanly with the molded article, and no material will be 7 left to clog the sprueway whenthe next shot is made.

As an illustrative example of one way of accomplishing such localized cooling, an ejector ll provides a reduced nose l2 projecting into the recess 8. The nose I2 is so proportioned that it will be surrounded on three sides by molded material within the recess 8, with the end of the nose located near where the sprue 9 is of greatest cross-section. The ejector II is hollow, so as to provide a chamber l3 closed at one end by a plug for circulating a cooling medium within the chamber l3, as for example, by means of a nozzle l5 discharging in the direction of the nose l2, with the wall of the chamber providing a discharge opening i6, to carry off the cooling medlum. The movable die 3 is partially cut away in the vicinity of the ejector I I, so as to permit the admission and discharge of the cooling medium to and from the chamber l3 through flexible conduits l'l, coincidentally with movement of the die 8, and of the ejector ll.

When the nozzle I delivers a charge of thermoplastic material under pressure, so asto completely fill the molding receses 6 and I, the runners 5 and the sprueway 2, the material in the recess 8 starts to cool, upon contact with the nose l2, and this cooling effect is rapidly communicated to the base of the sprue 9.- As a result ofthe accelerated cooling at the nose l2, the material within the recess 8 in the movable die 8, solidifies at least as fast as the material in the molding recesses 6 and I. Consequently,

- drawing movement, as shown. in Fig. 3, the vicinity of the sprueway 2, where it is more conwhen" the die 8 is moved away from the die 2,

to withdraw the molded articles, as shown in Fig. 2, the sprue 8 pulls cleanly out of the sprueway 2. As the'dle 3 reaches the limit of its with- 2 8,800,816 andpermittingitsdischargefromthemaehineby suitable means, not shown. The central portionoiamoldedarticleisshowninperspective in Hg. 4. from which it is evident that the base of the sprue I provides a recess lo, iormed'by the cooling nose II. w

from the iorqoing. it is apparent that by the present invention, there is provided an improved dle structure for plastic molding machines, char- .drawal of all material from the stationary die.

with the molded articles. As a direct result oi this cooling eflect, it is possible to operate the molding machine with the intervals between shots best timed to insure the desired degree oi solidity in the molded articles, rather than in the vicinity oi the sprue. I

I claim:

1. In combination, a stationary die and a movrounding said .in the vicinity of said sprueway. 2. In combination, a stationary die and a movable die deiining a molding cavity, a sprueway 5 extending from said cavity through the stationary.

die, means ior delivering heated plastic material to said cavity through said sprueway, a plunger carried by the movable die with a reduced nose portion thereof projecting into said die cavity in alignment with said sprueway, so that plastic material delivered through said sprueway will substantially surround said nose within the cavity. and means for cooling the nose portion of said plunger to accelerate the solidifying of 16 plasticmaterial in contact therewith.

3. In combination, a stationary die and a movable die defining a molding cavity, a sprueway extending from said cavity through the stationary die, means for delivering heated plastic ma- 20 terial to said cavity through said sprueway, a

plunger carried by the movable die with a reduced nose portion thereof projecting into said die cavity in alinement with "said sprueway, so that plastic material delivered through said sprueway able die defining a molding cavity, a sprueway ex-:: will substantially surround said nose within the tending from said cavity through the stationary die, means for delivering heated plastic material to said cavity through said sprueway; an election plunger carried by the movable die, with a portion projecting into said cavity in alinement with said sprueway, and means for cooling the-pro- 'iecting portion or said plimger to accelerate the I solidifying oimaterial within the cavity surcavity, and means for cooling the nose portion of said plunger to accelerate the solidifying of plastic material in contact therewith, movement of said plunger after the dies have opened serving to cause said plunger to clear the molded article from said dies, by reason of the support of said article on said plunger nose. s

' LEON 1". MARSH.

portiomaswellaswith-- 

